A triple stack is an Ecstasy tablet that is supposedly 3 layers of mdma, or 3x as much mdma in one tablet. As said by Erowid, triple stacks are usually no different and used as a marketing gimmick by dealers. E, triple stack or not, is usually about 10-30 dollars in pricing.

a maney ass white rapper from the bay he bang norte and he came from 24th street and capp street inmission district in SAN FRANSISCO, his namestriplestack because everybody in the bay stay smakcin themthizz pills and we only fuck with triple stacks